The broad objective of this work is to develop structural and chemical principles which make it possible to find highly specific ways to interfere with fundamental biological processes in the propagation of the HIV virus. Specific projects include the use of NMR methods for determination of the structure of peptide fragments of the HIV transactivating (Tat) protein with its RNA target, TAR. Building on our earlier demonstration of a long- lived and specific complex between a 24-amino acid peptide and a 27- nucleotide segment of TAR (deltaTAR), we will explore intensively the structure of this complex. Comparative studies will also be undertaken in which mutant deltaTAR RNAs with much reduced complex stability and lifetime are substituted for the wild type, and in which smaller peptide fragments containing the basic region of Tat are in complex with wild type deltaTAR. Stopped flow methods will be used to probe the possible role of the kinetics of peptide and RNA conformational changes in limiting the rate of complex formation. A second objective will be to assay for physical interaction between Tat bound to TAR and regulatory proteins, specifically Sp1, bound to promoter elements. Specially constructed bent DNA molecules which bring the Tat-TAR element into apposition with an Sp1 binding site will be used for this purpose. Finally, we will initiate studies of the ability of the enediyne class of compounds to modify or cleave viral proteins, specifically gp120. Preliminary work shows that these compounds are able to react with proteins, including apparent dimerization and cleavage events. Strategies will be developed for targeting cleavage reactions to the region of gp120 which is responsible for CD4 binding.